In recent years, molecules of oligosaccharides have attracted attention as third chain life molecules following nucleic acids (DNA) and proteins. The human body is a huge cell society comprising about 60 trillion cells, and the surfaces of all the cells are covered with oligosaccharide molecules. For example, ABO blood type are determined according to the difference of oligosaccharides over the surfaces of cells.
Oligosaccharides function in connection with the recognition of cells and interaction of cells and are key substances for the establishment of the cell society. Disturbances in the cell society lead, for example, to cancers, chronic diseases, infectious diseases and aging.
For example, it is known that when cells cancerate, changes occur in the structure of oligosaccharides. It is also known that Vibrio cholerae, influenza virus, etc. ingress into cells and cause infection by recognizing and attaching to a specific oligosaccharide.
Clarification of oligosaccharide functions leads to development of pharmaceuticals and foods based on novel principles, contributing to the prevention and therapy of diseases, and a wide variety of applications are expected of oligosaccharides.
Oligosaccharides are much more complex than DNA or proteins in structure because of the diversity of arrangements of monosaccharides, modes or sites of linkages, lengths of chains, modes of branches and overall structures of higher order. Accordingly, biological information derived from the structures thereof is more diversified than is the case with DNA and proteins. Although the importance of research on oligosaccharides has been recognized, the complexity and variety of structures thereof have delayed progress in the research on oligosaccharides unlike the studies on DNA and proteins.
Many of proteins present on the surfaces of cell membranes or in serum have oligosaccharides attached thereto as described above. The molecules wherein oligosaccharides are combined covalently with proteins are termed glycoproteins, which can be divided into two groups according to the difference in the mode of linkage between the oligosaccharide and the protein. Oligosaccharides of one type are asparagine-linked oligosaccharides (N-glycoside linkage type) wherein an amino group of the side chain of asparagine (Asn) is linked with the oligosaccharide. Oligosaccharides of the other type are mucin type oligosaccharides (O-glycosidic linkage type) wherein the oligosaccharide is linked with the alcohol of serine (Ser) or threonine (Thr). All the asparagine-linked oligosaccharides have a basic skeleton comprising five sugar moieties, and are divided into subgroups of high-mannose type, complex type and mixture type, according to the kind of the nonreducing terminal sugar moiety of the oligosaccharide linked. On the other hand, the mucin-liked oligosaccharides are divided into four groups according to the difference of the basic skeleton.
Although such oligosaccharides are important compounds, these compounds are insufficient in absolute amounts available. Methods of obtaining oligosaccharides include isolation of oligosaccharides only from glycoproteins which are present in the living body. However, it is difficult to cut off large quantities of oligosaccharides from glycoproteins. Further there are in the living body many oligosaccharides which closely resemble, and difficulty is encountered in obtaining a single oligosaccharide only in a large quantities. It is also difficult to obtain large quantities of oligosaccharides which are not present in the living body.
An object of the present invention is to provide a novel asparagine-linked oligosaccharide derivative containing at least one sialic acid or sialic acid derivative at a nonreducing terminal, and a process for preparing the same.
Another object of the invention is to provide a novel asparagine-linked oligosaccharide containing at least one sialic acid or sialic acid derivative at a nonreducing terminal, and a process for preparing the same.
Another object of the invention is to provide a novel oligosaccharide containing at least one sialic acid or sialic acid derivative at a nonreducing terminal, and a process for preparing the same.
An object of the present invention is to provide a novel asparagine-linked oligosaccharide derivative containing at least one fucose in N-acetylglucosamine on the nonreducing terminal side of an asparagine-linked oligosaccharide wherein the asparagine has amino group protected with a lipophilic (hydrophobic) protective group, and a process for preparing the derivative.